- Katherine K Matthay: Department of Pediatrics, UCSF School of Medicine, San Francisco, CA, USA. matthayk@peds.ucsf.edu
(131)I-metaiodobenzylguanidine (MIBG) is specifically taken up in neuroblastoma, with a response rate of 20%-37% in relapsed disease. Nonradioactive carrier MIBG molecules inhibit uptake of (131)I-MIBG, theoretically resulting in less tumor radiation and increased risk of cardiovascular toxicity. Our aim was to establish the maximum tolerated dose of no-carrier-added (NCA) (131)I-MIBG, with secondary aims of assessing tumor and organ dosimetry and overall response.
METHODS: Eligible patients were 1-30 y old with resistant neuroblastoma, (131)I-MIBG uptake, and cryopreserved hematopoietic stem cells. A diagnostic dose of NCA (131)I-MIBG was followed by 3 dosimetry scans to assess radiation dose to critical organs and soft-tissue tumors. The treatment dose of NCA (131)I-MIBG (specific activity, 165 MBq/��g) was adjusted as necessary on the basis of critical organ tolerance limits. Autologous hematopoietic stem cells were infused 14 d after therapy to abrogate prolonged myelosuppression. Response and toxicity were evaluated on day 60. The NCA (131)I-MIBG was escalated from 444 to 777 MBq/kg (12-21 mCi/kg) using a 3 + 3 design. Dose-limiting toxicity (DLT) was failure to reconstitute neutrophils to greater than 500/��L within 28 d or platelets to greater than 20,000/��L within 56 d, or grade 3 or 4 nonhematologic toxicity by Common Terminology Criteria for Adverse Events (version 3.0) except for predefined exclusions.
RESULTS: Three patients each were evaluable at 444, 555, and 666 MBq/kg without DLT. The dose of 777 MBq/kg dose was not feasible because of organ dosimetry limits; however, 3 assigned patients were evaluable for a received dose of 666 MBq/kg, providing a total of 6 patients evaluable for toxicity at 666 MBq/kg without DLT. Mean whole-body radiation was 0.23 mGy/MBq, and mean organ doses were 0.92, 0.82, and 1.2 mGy/MBq of MIBG for the liver, lung, and kidney, respectively. Eight patients had 13 soft-tissue lesions with tumor-absorbed doses of 26-378 Gy. Four of 15 patients had a complete (n = 1) or partial (n = 3) response, 1 had a mixed response, 4 had stable disease, and 6 had progressive disease.
CONCLUSION: NCA (131)I-MIBG with autologous peripheral blood stem cell transplantation is feasible at 666 MBq/kg without significant nonhematologic toxicity and with promising activity.